ICF高功率激光驱动器中受激拉曼散射效应研究
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摘要
在惯性约束聚变(ICF)中,受激拉曼(SRS)效应是一种非常有害的非线性效应。在ICF高功率激光驱动器中,SRS效应产生最明显的环节是频率转换系统和空气长程传输系统。对于频率转换系统中的大口径频率转换晶体来说,在垂直于泵浦光传播方向产生的横向受激拉曼散射(TSRS)是最具破坏性的非线性效应。TSRS效应不仅会造成泵浦光能量严重损失,使倍频效率大大降低,更严重的是,当TSRS产生的斯托克斯光的峰值能量密度大于频率转换晶体的破坏阈值时,将会造成频率转换晶体永久性破坏。此外,由频率转换器输出的三倍频强紫外激光在空气长程传输过程中将产生沿泵浦光传输方向的受激旋转拉曼散射(SRRS)效应,SRRS效应不但会引起泵浦光能量的损失,而且还将导致激光光束质量明显变差,从而影响激光打靶的质量。因此,为了提高ICF高功率激光驱动器运行的可靠性、稳定性,最终顺利实现聚变点火,必须对ICF高功率激光驱动器中产生的SRS效应进行研究。
本论文针对ICF高功率激光驱动器中产生的受激拉曼散射效应,详细讨论了频率转换系统和空气长程传输系统中SRS效应对频率转换晶体以及激光光束质量等方面的影响。论文取得的主要结果包括:
(1)建立了强激光通过不同介质传输时产生SRS效应的物理模型
针对ICF高功率激光驱动器中谐波转换晶体和空气两种不同的传输介质,从量子力学的角度出发,建立了SRS效应的物理模型,详细考虑了Stokes光和泵浦光的衍射、Langevin(郎兹万)噪声源、晶体表面和端面反射、介质的非线性极化、泵浦光的衰减、斯托克斯光的非线性放大以及拉曼线宽等诸多因素。
(2)对谐波转换晶体中的TSRS效应特性进行研究
针对ICF驱动器的不同运行状态(常规运行和长脉冲运行),讨论了KDP和
In inertial confinement fusion (ICF), stimulated Raman scattering (SRS) is an extremely harmful nonlinear effect, which will produce significantly in the frequency conversion system and long air path propagation of high-power laser driver. For the frequency conversion crystals of large aperture, the transverse stimulated Raman scattering (TSRS) is the most damaging nonlinear effect, which will lead to the loss of laser energy and the degradation of the frequency conversion efficiency. When the peak Stokes fluence exceed the damage threshold of frequency conversion crystals, the fatal damage on the crystals are the most serious. Furthermore, owing to the effect of stimulated rotational Raman scattering (SRRS) on 3ω high-power ultraviolet laser beams in the process of long air path propagation after the frequency conversion system, not only laser energy losses, but also the beam quality degrades, leading to the effect on target irradiation. For improving the reliability, stability of laser driver and realizing laser fusion successfully, it is essential to study the SRS effect of high-power laser driver for ICF.In the thesis, the effect of SRS on the crystals and beam quality in the frequency conversion system and long air path propagation has been discussed in detail. The main results obtained can be summarized as follows: (1) The physical model of SRS in different mediums has been built up.Based on quantum-mechanical viewpoints, the physical model of SRS effect has been built up for two different mediums: frequency conversion crystals and air in ICF, which considered the diffraction effects of Stokes and pump lasers, Langevin noise sources, reflection at the faces and the edges of crystals, the nonlinear polarization of the medium, the depletion of pumped laser, the nonlinear
amplification of the Stokes field and the Raman bandwidth, ect.(2) The characteristics of TSRS effect in frequency conversion crystals have been studied.For different operating conditions of laser driver: long and short pulse, TSRS effect in KDP and KD*P crystals has been studied. The effect of the temporal phase modulation on peak Stokes intensity, peak Stokes fluence and space-time characteristic of TSRS has been calculated and analyzed.(3) The SRRS effect in the process of high-power ultraviolet laser propagationin long air path has been studied.The SRRS effect in the process of high-power ultraviolet laser propagation in long air path has been studied quantitatively. The effect of the factors including the spatial phase perturbation and vacuum on the SRRS threshold, Stokes temporal characteristic, SRRS conversion efficiency and laser beam quality has been calculated and analyzed.
本论文针对ICF高功率激光驱动器中产生的受激拉曼散射效应,详细讨论了频率转换系统和空气长程传输系统中SRS效应对频率转换晶体以及激光光束质量等方面的影响。论文取得的主要结果包括:
(1)建立了强激光通过不同介质传输时产生SRS效应的物理模型
针对ICF高功率激光驱动器中谐波转换晶体和空气两种不同的传输介质,从量子力学的角度出发,建立了SRS效应的物理模型,详细考虑了Stokes光和泵浦光的衍射、Langevin(郎兹万)噪声源、晶体表面和端面反射、介质的非线性极化、泵浦光的衰减、斯托克斯光的非线性放大以及拉曼线宽等诸多因素。
(2)对谐波转换晶体中的TSRS效应特性进行研究
针对ICF驱动器的不同运行状态(常规运行和长脉冲运行),讨论了KDP和
In inertial confinement fusion (ICF), stimulated Raman scattering (SRS) is an extremely harmful nonlinear effect, which will produce significantly in the frequency conversion system and long air path propagation of high-power laser driver. For the frequency conversion crystals of large aperture, the transverse stimulated Raman scattering (TSRS) is the most damaging nonlinear effect, which will lead to the loss of laser energy and the degradation of the frequency conversion efficiency. When the peak Stokes fluence exceed the damage threshold of frequency conversion crystals, the fatal damage on the crystals are the most serious. Furthermore, owing to the effect of stimulated rotational Raman scattering (SRRS) on 3ω high-power ultraviolet laser beams in the process of long air path propagation after the frequency conversion system, not only laser energy losses, but also the beam quality degrades, leading to the effect on target irradiation. For improving the reliability, stability of laser driver and realizing laser fusion successfully, it is essential to study the SRS effect of high-power laser driver for ICF.In the thesis, the effect of SRS on the crystals and beam quality in the frequency conversion system and long air path propagation has been discussed in detail. The main results obtained can be summarized as follows: (1) The physical model of SRS in different mediums has been built up.Based on quantum-mechanical viewpoints, the physical model of SRS effect has been built up for two different mediums: frequency conversion crystals and air in ICF, which considered the diffraction effects of Stokes and pump lasers, Langevin noise sources, reflection at the faces and the edges of crystals, the nonlinear polarization of the medium, the depletion of pumped laser, the nonlinear
amplification of the Stokes field and the Raman bandwidth, ect.(2) The characteristics of TSRS effect in frequency conversion crystals have been studied.For different operating conditions of laser driver: long and short pulse, TSRS effect in KDP and KD*P crystals has been studied. The effect of the temporal phase modulation on peak Stokes intensity, peak Stokes fluence and space-time characteristic of TSRS has been calculated and analyzed.(3) The SRRS effect in the process of high-power ultraviolet laser propagationin long air path has been studied.The SRRS effect in the process of high-power ultraviolet laser propagation in long air path has been studied quantitatively. The effect of the factors including the spatial phase perturbation and vacuum on the SRRS threshold, Stokes temporal characteristic, SRRS conversion efficiency and laser beam quality has been calculated and analyzed.
引文
[1.1] 张彬,《四川大学博士学位论文》,四川大学,1995年.
[1.2] 彭翰生,《惯性约束聚变和高功率激光技术》,中国工程物理研究院,1995年.
[1.3] H.E巴索夫等,《稠密等离子体诊断学》,《强激光与粒子束》杂志社,1992年12月第一版.
[1.4] 常铁强,《激光聚变靶物理简介》,北京应用物理与计算数学研究所,2003年.
[1.5] 朱少平,《惯性约束聚变研究介绍》,北京应用物理与计算数学研究所.
[1.6] 王淦昌,《激光惯性约束核聚变(ICF)最新进展简述》,核科学与工程,1997年9月,Vol.17,No.3:266～269.
[1.7] 王恭明,钱士雄,《非线性光学—原理与进展》,2001年.
[1.8] 李大义,《非线性光学》,2001年.
[1. 9] Michel L. Andre. Status of the LMJ project. SPIE, Vol.3047: 38～42.
[1. 10] P. Wegner, J. Auerbach, T. Biesiada, S. Dixit, J. Lawson, J. Menapace, T. Parham,D. Swift, P. Whitman, W. Williams. NIF final optics system: frequency conversion and beam conditioning. LLNL.
[1. 11] Ying L and Terrance K. Raman scattering in air: A four-dimensional system analysis. SPIE, 1992, 1625: 158-166.
[1. 12] Ying L, Terrance K and J J Armstrong. Laser system power balance effects from stimulated rotational Raman scattering in air. SPIE, 1992, 1870: 14-25.
[1. 13] V.A.Eroshenko, S.V.Bondareokn, et al... Computer modeling of transverse SBS in a anisotropic crystals. SPIE, 1995 v2633: 691-699.
[1. 14] Rokni M. Rotational stimulated Raman scattering in atmospheric propagation. Avco Everett Research Laboratory Report AMP, 1984: 663.
[1. 15] Bruce Oldaker, Timothy Pritchett and Thomas Moore. Stimulated Rotational Raman Scattering in H_2, SPIE, 1996, Vol.2700: 382～389.
[1. 16] R.A.Sacks, C.E.Barker, R.B.Erlich. ICF Quarterly Report. LLNL, 1992,v2, №4: 179.
[1. 17] R.A.Sacks, C.E.Barker, J.A.Caird, et al. Transverse stimulated Raman scattering in KDP. SPIE, 1995 v2633: 501-505.
[1.2] 彭翰生,《惯性约束聚变和高功率激光技术》,中国工程物理研究院,1995年.
[1.3] H.E巴索夫等,《稠密等离子体诊断学》,《强激光与粒子束》杂志社,1992年12月第一版.
[1.4] 常铁强,《激光聚变靶物理简介》,北京应用物理与计算数学研究所,2003年.
[1.5] 朱少平,《惯性约束聚变研究介绍》,北京应用物理与计算数学研究所.
[1.6] 王淦昌,《激光惯性约束核聚变(ICF)最新进展简述》,核科学与工程,1997年9月,Vol.17,No.3:266～269.
[1.7] 王恭明,钱士雄,《非线性光学—原理与进展》,2001年.
[1.8] 李大义,《非线性光学》,2001年.
[1. 9] Michel L. Andre. Status of the LMJ project. SPIE, Vol.3047: 38～42.
[1. 10] P. Wegner, J. Auerbach, T. Biesiada, S. Dixit, J. Lawson, J. Menapace, T. Parham,D. Swift, P. Whitman, W. Williams. NIF final optics system: frequency conversion and beam conditioning. LLNL.
[1. 11] Ying L and Terrance K. Raman scattering in air: A four-dimensional system analysis. SPIE, 1992, 1625: 158-166.
[1. 12] Ying L, Terrance K and J J Armstrong. Laser system power balance effects from stimulated rotational Raman scattering in air. SPIE, 1992, 1870: 14-25.
[1. 13] V.A.Eroshenko, S.V.Bondareokn, et al... Computer modeling of transverse SBS in a anisotropic crystals. SPIE, 1995 v2633: 691-699.
[1. 14] Rokni M. Rotational stimulated Raman scattering in atmospheric propagation. Avco Everett Research Laboratory Report AMP, 1984: 663.
[1. 15] Bruce Oldaker, Timothy Pritchett and Thomas Moore. Stimulated Rotational Raman Scattering in H_2, SPIE, 1996, Vol.2700: 382～389.
[1. 16] R.A.Sacks, C.E.Barker, R.B.Erlich. ICF Quarterly Report. LLNL, 1992,v2, №4: 179.
[1. 17] R.A.Sacks, C.E.Barker, J.A.Caird, et al. Transverse stimulated Raman scattering in KDP. SPIE, 1995 v2633: 501-505.